If you want to lease the home without a purchase you can approach the listing agent but, truthfully they may not be too receptive. Their position will be that they home is for sale. It will really depend on the financial situation with the owner. If you want to maybe explore the possibility of a lease/purchase then they maybe able to work out a deal with you. If that is the case you would most likely want to get your own buyers agent to help you through this and make sure you are protected. Dale is correct though that a 3 year lease is a long time for a home that is presently for sale.
Hope this helps,